Well-drilling method



United States Patent 3,373,105 WELL-DRILLENG METHGD John B Lister, Scottsdale, Ariz., and Victor A. Rundlc, Oakland, Calif., assignors to Seepage Control, inc., Phoenix, Ariz., a corporation of Arizona No Drawing. Filed Apr. 8, 1965, Ser. No. 446,713 Claims. (Cl. 2528.5)

ABSTRACT OF THE DHSCLOSURE A method of drilling a borehole through an earth formation containing strata which tend to absorb water and swell or slough using an aqueous drilling fluid such as brine or water to which has been added a minor quantity of an emulsion of petroleum wax.

This invention relates to an improved method for drilling oil wells; more particularly, to an improved method for drilling wells which traverse a stratum of shale having a tendency to absorb water and slough into the borehole.

In a large proportion of the oil wells drilled, it is the practice to circulate water or brine in the borehole to remove the cuttings and to delay circulation of a drilling mud in the borehole until mud circulation must be resorted to either to contain formation pressure or to minimize sloughing of water absorbent shale into the borehole. Where formation pressures dictate the use of mud, there is no alternative. If, however, mud circulation is commenced in order to prevent sloughing of shale, then the method of this invention permits postponement of the initiation of mud circulation and extends the period during which water or brine may be circulated as the drilling fluid with attendant higher penetration rates at a given power input and an over-all reduction of mud costs at completion.

A small proportion of wells are drilled circulating air through the borehole to remove cuttings. When moderate water intrusion is encountered, mist drilling is resorted to, i.e., air drilling is continued and a small amount of a foaming agent is introduced into the borehole with the air stream, the cuttings are then carried from the borehole by the air stream and the intruding water is carri'ed out by the air stream as a foam, or mist. If, however, the borehole has traversed a stratum of shale characterized by a tendency to absorb water and slough into the borehole before water intrusion is encountered, the foam eiiiuent from the borehole may wet the shale, sloughinrg may begin, and recourse to circulation of drilling mud may be required. The method of the present invention prevents such sloughing and makes it possible to drill with air for a longer period before mudding up.

Pursuant to the present invention, a small amount of paraffin wax dispersed in an aqueous fluid is introduced into the borehole as the drilling process proceeds. The wax dispersion is introduced continuously or semicontinuously at a rate such that the total quantity of wax introduced is at least 0.0075 pound of wax per square foot of interior surface of the borehole; amounts in the range of about 0.0075 to 0.15 pound of wax per square foot of interior borehole surface are generally completely adequate. Larger amounts can be used, but little incremental benefit attaches to the use of very large amounts, for example, amounts in excess of 0.5 pound per square foot of interior borehole surface. Pursuant to a more specific embodiment of the invention, an aqueous dispersion of wax is added to a drilling fluid selected from the group consisting of water and brine in an amount sufficient to give the drilling fluid a dispersed wax content at least about 0.0005% by weight. Wax contents in the range about 0.0005 to 0.01% are satisfactory and wax contents in the range about 0.001 to 005% by weight are preferred. Larger wax contents may be employed, but little if any incremental benefit attaches to the employ: ment of fluids having very high Wax contents, for example, above 0.05% by weight.

Introduction of the wax dispersion may be, and desirably is, begun when the hole is started and continued throughout the drilling operation; one of the principal benefits of the practice of the invention will be realized, however, if introduction of the wax dispersion is delayed until the borehole has begun to penetrate a shale stratum which tends to absorb water and slough and continued thereafter.

In a representative drilling operation in which either water or brine is employed as the drilling fluid, about 0.5 to 5.0 gallons of a wax emulsion having a wax content of about 2.5 to 3.5 pounds per gallon is passed down the drill stern each hour with the aqueous drilling fluid so that it passes over the surface of the bit as the drilling proceeds. Introduction of the wax emulsion at a reasonably constant rate is facilitated if the one gallon of wax emulsion is mixed with a relatively large volume of water, for instance, with 50 gallons of water, and the diluted emulsion is passed down the drill stem during the 1 hour drilling period.

Illustrative of wax emulsions suitable for use in the practice of the invention are the following:

Emulsion A.--An emulsion containing 28% by weight of l541,.56 F. AMP petroleum wax, 0.5% by weight of Tween 40, 1.5% by weight of Arquad T50, and 70% by weight of water. Arquad T 50 is an organo trimethyl quaternary ammonium chloride in which the organo radical consists of a mixture of tetradecyl (3%), hexadecyl (27%), octadecyl (16%), octadecenyl (48%) and octadecadienyl (6%). Tween 40 is a poiyoxyethylene derivative of sorbitan monopalmitate.

Emulsion B.An emulsion suitable for use in the practice of the invention was prepared as follows:

Mixture l was prepared by blending 2.5 grams of Carbopol 934 (a polycarboxylated polymethylene) and 2120 grams of water with violent agitation for a period of 30 minutes at ambient temperature, after which there was added 12.5 grams of Tween 40 and 3.4 grams of triethanolamine, and the resulting mixture was heated to a temperature of 200 F.

Mixture 2 was prepared by blending 12.5 grams of oleic acid and 350 grams of petroleum paratfin wax having a melting point range of l25130 F. AMP, and heating to a temperature of 200 F.

Mixture 2 was slowly added to mixture 1 at 200 F. with violent agitation, resulting in an aqueous wax dis persion concentrate.

Emulsion C.An emulsion suitable for use in the practice of the invention was prepared as follows:

Mixture l was prepared by blending 12.5 grams of Tween 40, 3.4 grams of triethanolamine, 2.5 grams of Carbopol 934, and 2120 grams of water at 200 F. with agitation.

Mixture 2 was prepared by blending 175 grams of paraflin wax having a melting point range of 130 F. AMP, 175 grams of a waxy residum from slack wax having a melting point range of 177 F. and 12.5 grams of oleic acid by heating to 200 F. with agitation.

Mixture 2 was slowly poured into mixture 1 with violent agitation at 200 F. The resulting dispersion served as a concentrate.

Emulsion D.An emulsion suitable for use in the practice of the invention was prepared as follows:

Mixture 1 was prepared by blending 2120 grams of 3 Water, 3.4 grams of triethanolamine, 12.5 grams of Tween 40, and 2.5 grams of Carbopol 934 at 200 F.

Mixture 2 was prepared by blending 350 grams of a waxy distillate from a Minas crude, and 12.5 grams of oleic acid with agitation at 200 F.

Mixture 2 was slowly poured into mixture 1 with violent agitation at 200 F. to form the desired wax dispersion.

Generally, wax dispersion concentrates suitable for use in the practice of the invention contain 14 to 35% by Weight of petroleum wax having a melting point in the range 100 to 190 F. AMP, desirably in the range 125 to 165 F. AMP, from about 0.4 to 4.5% by weight of a dispersing agent or agents, and from 60.5 to 85.6% by weight of water. The character of the dispersing agent is not a critical feature of suitable dispersions and the dispersing agent may be either anionic, cationic, nonionic, nonionic-cationic mixtures, or nonionic-anionic mixtures. For wide spread use in a variety of formations and formation waters, the nonionic-cationic combinations are preferred.

While it is generally preferred to introduce the abovedescribed emulsions suitably diluted with water or brine directly into the drill stem and through it into contact with the bit, the wax dispersion may be added to the drilling fluid, water or brine, contained in the surface pit from which the fluid is introduced into the borehole and to which the efiiuent fluid containing cuttings is discharged from the borehole, When the wax dispersion is added in this manner an incremental benefit may be obtained in that the pit is sealed by the wax against leakage or seepage.

The most significant benefit derived from the practice of the invention is the prevention of sloughing of shales during a drilling operation in which water or brine is used as the drilling fluid. Other beneficial effects, however, have been observed in the course of the practice of the invention in drilling formations that present no sloughing shale problem. Principally it has been observed that there is a substantial decrease in the torque of the drill stern and increased drilling rates have been experienced.

Several wells have been drilled using brine as the drilling fluid in the Midland, Tex. area. In this area a red bed formation which is a mass of red clay usually from 800 to 1000 feet thick must be traversed by the borehole. This red clay has a tendency to swell and slough off on contact with water. Several 8-inch diameter wells were drilled at a rate about 800 feet per day using brine as the drilling fluid. The brine was circulated through the borehole at the rate of 200 to 250 gallons per minute and 1 gallon per hour of Emulsion A, above, was introduced into the brine entering the drill stern. No sloughing of shale was experienced and it was possible to penetrate the red bed layer and continue beyond it without recourse to the use of mud.

While introduction of wax emulsion having a wax content from 2.5 to 3.5 pounds per gallon at the rate of one gallon per hour or in the range 0.5 to gallons per hour will ordinarily give adequate control of sloughing shales, there are some shales which are especially sensitive to water and exhibit extreme sloughing tendencies. In drilling through such sensitive shale strata it may be necessary to introduce the wax emulsion at higher rates such as 10 to gallons per hour and in a few instances at rates about gallons per hour (about 90 pounds per hour of wax) to suppress the tendency of the shale to slough to the extent that the strata may be penetrated using a low solids aqueous drilling fluid, or water or brine.

A well was drilled in western Oklahoma, penetrating a formation that had several shale strata which tended to slough. Wax dispersion was introduced into the brine which was employed as the drilling fluid in amount sufficient to give the brine a wax content approximately 0.004% by weight. At 4700 feet, shale strata normally tending to slough had been passed through without difiiculty and at this depth the well was two days ahead of schedule based on drilling experience in that area.

In an air drilling operation conducted in the Midland, Tex. area, water encroachment was encountered and a detergent was injected to commence the mist drilling technique. The borehole had already penetrated a shale stratum having a tendency to absorb water and slough into the hole, and after mist drilling got under way theupper shale formation commenced heaving and threatened to stick the drill stern. It appeared that a conventional mud system would be required to finish the hole. However, dispersed wax was passed down the drill stem together with the air and detergent. Shortly after the introduction of the wax dispersion there was no further evidence of heaving and the drilling operation was successfully completed without having to go to a mud system.

The invention has also been practiced by introducing the wax dispersion into the reserve brine pit at the well head. Makeup aqueous drilling fluid is introduced into the well from this pit. Introduction of from about one-half to one gallon of Emulsion A, described above, per square yard of brine pit interior surface performs the dual function of sealing the brine pit against seepage and providing the drilling fluid with a dispersed wax content in excess of 0.0005% by weight as required to obtain improved drilling performance.

We claim:

1. In a method of drilling a well through sloughing formations, with an aqueous drilling fluid selected from the group consisting of water and brine, the improvement comprising introducing a minor amount of petroleum wax dispersed in an aqueous carrier into said drilling fluid to prevent sloughing of the formations penetrated by the well, the quantity of wax introduced being at least 0.0075 pound of wax per square foot of interior borehole surface of borehole drilled while the wax dispersion is being introduced.

2. In a method of drilling a well into the earth with an aqueous drilling fluid selected from the group consisting of water and brine, the improvement comprising adding to the drilling fluid being introduce-d into the well between 0.5 and 25 gallons per hour of a petroleum wax emulsion having a wax content of between 2.5 and 3.5 pounds per gallon.

3. In the process of drilling boreholes into earth formatrons using a drilling fluid selected from the group consisting of water and brine, the improvement which comprises introducing into thesaid drilling fluid during the drilling operation a minor amount of petroleum Wax dispersed in an aqueous fluid, the quantity of wax introduced being at least .0075 pound of wax per square foot of interior borehole surface of borehole drilled during the period of wax dispersion introduction.

4. In the process of drilling boreholes into earth formatrons using a drilling fluid selected from the group consistmg of water and brine, the improvement which comprises continually introducing into said drilling fluid during the drilling operation a minor amount of petroleum wax, having a melting point above F., dispersed in an aqueous fluid, the total quantity of wax introduced being at least 0.0075 pound per square foot of interior bore-- hole surface.

5. The method as described in claim 4, wherein the quantity of petroleum wax introduced into the borehole is in the range about 0.015 to 0.5 pound per square foot of interior borehole surface.

6. In a process for drilling a borehole traversing a shale stratum characterized by a tendency to absorb water and slough into the borehole, using a drilling fluid selected from the group consisting of water and brine, the improvement which comprises injecting into the borehole during the drilling process an aqueous dispersion of paraflin wax, the quantity of dispersed wax injected being at least sufficient to give the drilling fluid injected into the borehole a wax content of 0.0005% by weight.

7. The method as described in claim 6, wherein the quantity of dispersed wax injected into the borehole is suflicient to give the drilling fluid injected into the borehole a wax content in the range .001 to .05 by weight.

8. In a process for drilling a borehole into an earth formation containing a stratum of shale having a tendency to absorb water and slough using a drilling fluid selected from the group consisting of water and brine, the improvement which comprises continually introducing into said drilling fluid a minor amount of paraflin wax dispersed in an aqueous medium at least during the portion of the drilling process during which the borehole passes through the shale stratum, the quantity of wax introduced being in the range about 0.0075 to 0.15 pound per square foot of interior surface of the borehole drilled during the period of dispersed wax introduction.

9. In the process of drilling a borehole through a stratum of shale characterized by a tendency to absorb water and slough using a drilling fluid selected from the group consisting of water and brine, the improvement which 20 comprises introducing from 0.5 to 25 gallons of an aqueous emulsion of petroleum wax having a wax content in the range about 2.5 to 3.5 pounds per gallon into said drilling fluid each hour during the period required to drill through the shale stratum.

10. In a process for drilling a borehole through a shale stratum characterized by a tendency to absorb water and slough using a drilling fluid selected from the group consisting of water and brine, the improvement which comprises introducing from about 1 to about 90 pounds per hour of petroleum wax dispersed in an aqueous medium into said drilling fluid at a point near the drill bit.

References Cited UNITED STATES PATENTS 2,209,591 7/1940 Barnes 2528.5 2,425,768 8/1947 Wagner 25285 2,589,949 3/1952 Meadors 2528.5

FOREIGN PATENTS 934,165 8/1963 Great Britain.

LEON D. ROSDOL, Primary Examiner. HERBERT B. GUYNN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE-OF CORRECTION Patent No. 3,373,106 March 12, 1968 John B. Lister et a1 It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, lines 4 and 5 "assignors to Seepage Control Inc Phoenix, Ariz a corporation of Arizona' s hould read said Lister 'gassignor to Seepage Control, Inc., Phoenix, Ariz., a

corporation of Arizona and said Rundle assi'gnor to Chevron Research Company, San Francisco, Calif. a corporation of Delaware Signed and sealed this 4th day of November 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR;

Fletcher, Jr.

Commissioner of Patents Attesting Officer 

